This invention relates to a process for the removal of metals, in particular organically-bound calcium, from metals-containing petroleum crudes or heavy hydrocarbonaceous residua using sulfuric acid or its salts, particularly ammonium sulfate, as a demetalating agent. A few, but increasingly important, petroleum crude feedstocks, residua, and deasphalted oil derived from them, contain levels of calcium or other Group IIA metals which render them difficult, if not impossible, to process using conventional refining techniques. The metals contaminants causing particular problems are in the form of organically-bound, non-porphrynic compounds. These species have been attributed to, among other sources, naturally-occurring calcium. One class of calcium compounds identified in particular is the respective naphthenates and their homologous series. These organometallic compounds are not separated from the feedstock by normal desalting processes, and in a conventional refining technique they can cause the very rapid deactivation of hydroprocessing catalysts. Feedstocks demonstrating objectionably high levels of organically-bound calcium compounds are relatively unique, and include crudes from China, such as Shengli No. 2, and a few from the San Joaquin Valley in California. The residuum from these crudes also contains undesirably high levels of calcium.
The problems presented by organic calcium in petroleum feedstocks and the necessity for their removal have only been recently appreciated, and the prior art contains few references specifically to their removal. Metals removal generally, however, has been addressed in the prior art, specifically for the removal of known metallic contaminants, such as nickel, vanadium, and/or copper, which are ordinarily found in feedstocks as porphyrins and asphaltenes.
In U.S. Pat. No. 3,153,623, Eldib et al, selected commercially available organic compounds of high dielectric strength were added to assist in a process basically encompassing the electrically-directed precipitation of metals. U.S. Pat. No. 4,439,345, Duke, discloses the use of carboxylic acids to demulsify by demetalation the middle phase emulsion of an enhanced oil recovery product. U.S. Pat. No. 4,645,589, Krambeck, et al. discloses a method for removing vanadium and nickel metal porphyrins from hydrocarbon oils using phosphoric acid and its salts. U.S. Pat. No. 2,778,777, Powell, teaches the use of relatively high concentrations of sulfuric acid for the removal of porphyrinic heavy metals, such as vanadium, nickel and iron. Powell also teaches the removal of inorganic metal salts of light metals, such as calcium, sodium, and magnesium, also using relatively high concentrations of sulfuric acid, and ordinary desalting technology.
In U.S. applications Ser. Nos. 901,341, now U.S. Pat. No. 4,778,589, 901,342 now U.S. Pat. No. 4,778,591, 901,343 now U.S. Pat. No. 4,789,463, 901,344 now U.S. Pat. No. 4,778,590, 901,345 now U.S. Pat. No. 4,778,592 and 164,597 now U.S. Pat. No. 4,853,109, commonly assigned to the assignee of the present invention, various agents including aminocarboxylic acids, hydoxocarboxylic acids, dibasic carboxylic acids, and carbonic acid, and their salts, are used in similar processes to remove non-porphyrin organometallic contaminants from hydrocarbonaceous feedstocks.
Japanese Patent Publication Sho 52-30284, Fushimi, teaches a method for removing various metals contaminants from crude oil using a combination of mineral acid, alkyl phosphate ester and an oxidant. Japanese Patent Publication Sho 47-22947 teaches a lower level of metals removal using a combination of alkyl phosphate esters and alkyl carboxylic acid in the presence of mineral acids.
U.S. Pat. No. 4,432,865, Norman, teaches a process for treating used motor oil to remove metals using a polyhydroxy compound and a polyfunctional mineral acid.
Among other factors, it has now been unexpectedly found that organically-bound Group IIA metal contaminants, particularly those containing calcium, which are not separated using ordinary desalter technology, may be effectively removed from hydrocarbon feedstocks by mixing the metal compounds with a solution of sulfuric acid and/or its salts, particularly ammonium sulfate and ammonium bisulfate, and removing them from the feedstock by aqueous extraction and/or precipitation.